Alkoxylated fatty esters are normally manufactured by inserting of one or more alkylene oxide units, usually ethylene oxide (EO), between the oxygen and CH3 portions of a methoxy group of a methyl ester using mixed oxide catalysts, typically magnesium-containing oxides (see, e.g., U.S. Pat. Nos. 5,817,844, 6,184,400, and 6,504,061). They can also be made by esterifying fatty acids (or transesterifying fatty esters of lower alcohols) with alkoxylated alcohols. In yet another method, the alkoxylated fatty esters can be made by alkoxylating fatty acids with alkylene oxides, followed by etherification of the terminal hydroxyl group.
The performance characteristics of alkoxylated fatty esters will depend on the nature of the starting fatty methyl ester or fatty acid and the proportion, kind, and distribution of oxyalkylene groups. Alkoxylated fatty esters are valuable as nonionic surfactants and as additives for a wide variety of end-use applications, including, for example agricultural uses (see U.S. Pat. No. 6,068,849 and U.S. Pat. Appl. Publ. Nos. 2007/0032382 and 2008/0175930), hard surface cleaners (U.S. Pat. Nos. 7,270,131 and 5,386,045), laundry detergent boosters (U.S. Pat. No. 7,098,175), and other detergent applications (U.S. Pat. Nos. 6,303,564, 6,395,694, and 5,753,606).
The fatty acids or esters used to make alkoxylated fatty esters and derivatives are usually made by hydrolysis or transesterification of triglycerides, which are typically animal or vegetable fats. Consequently, the fatty portion of the acid or ester will typically have 6-22 carbons with a mixture of saturated and internally unsaturated chains. Depending on source, the fatty acid or ester often has a preponderance of C16 to C22 component. For instance, methanolysis of soybean oil provides the saturated methyl esters of palmitic (C16) and stearic (C18) acids and the unsaturated methyl esters of oleic (C18 mono-unsaturated), linoleic (C18 di-unsaturated), and α-linolenic (C18 tri-unsaturated) acids. The unsaturation in these acids has either exclusively or predominantly cis-configuration.
Recent improvements in metathesis catalysts (see J. C. Mol, Green Chem. 4 (2002) 5) provide an opportunity to generate reduced chain length, monounsaturated feedstocks, which are valuable for making detergents and surfactants, from C16 to C22-rich natural oils such as soybean oil or palm oil. Soybean oil and palm oil can be more economical than, for example, coconut oil, which is a traditional starting material for making detergents. As Professor Mol explains, metathesis relies on conversion of olefins into new products by rupture and reformation of carbon-carbon double bonds mediated by transition metal carbene complexes. Self-metathesis of an unsaturated fatty ester can provide an equilibrium mixture of starting material, an internally unsaturated hydrocarbon, and an unsaturated diester. For instance, methyl oleate (methyl cis-9-octadecenoate) is partially converted to 9-octadecene and dimethyl 9-octadecene-1,18-dioate, with both products consisting predominantly of the trans-isomer. Metathesis effectively isomerizes the cis-double bond of methyl oleate to give an equilibrium mixture of cis- and trans-isomers in both the “unconverted” starting material and the metathesis products, with the trans-isomers predominating.
Cross-metathesis of unsaturated fatty esters with olefins generates new olefins and new unsaturated esters that can have reduced chain length and that may be difficult to make otherwise. For instance, cross-metathesis of methyl oleate and 3-hexene provides 3-dodecene and methyl 9-dodecenoate (see also U.S. Pat. No. 4,545,941). Terminal olefins are particularly desirable synthetic targets, and Elevance Renewable Sciences, Inc. recently described an improved way to prepare them by cross-metathesis of an internal olefin and an α-olefin in the presence of a ruthenium alkylidene catalyst (see U.S. Pat. Appl. Publ. No. 2010/0145086). A variety of cross-metathesis reactions involving an α-olefin and an unsaturated fatty ester (as the internal olefin source) are described. Thus, for example, reaction of soybean oil with propylene followed by hydrolysis gives, among other things, 1-decene, 2-undecenes, 9-decenoic acid, and 9-undecenoic acid. Despite the availability (from cross-metathesis of natural oils and olefins) of unsaturated fatty esters having reduced chain length and/or predominantly trans-configuration of the unsaturation, alkoxylated fatty esters and their derivatives made from these feedstocks appear to be unknown. Moreover, alkoxylated fatty esters and their derivatives have not been made from the C18 unsaturated diesters that can be made readily by self-metathesis of a natural oil.
In sum, traditional sources of fatty acids and esters used for making alkoxylated fatty esters and their derivatives generally have predominantly (or exclusively) cis-isomers and lack relatively short-chain (e.g., C10 or C12) unsaturated fatty portions. Metathesis chemistry provides an opportunity to generate precursors having shorter chains and mostly trans-isomers, which could impart improved performance when the precursors are converted to downstream compositions (e.g., in surfactants). New C18 difunctional alkoxylated fatty esters and derivatives are also potentially available from oil or C10 unsaturated acid or ester self-metathesis. In addition to an expanded variety of precursors, the unsaturation present in the precursors allows for further functionalization, e.g., by sulfonation or sulfitation.